Background: Polymyositis and dermatomyositis in association with malignancy are paraneoplastic syndromes, but the incidence, treatment and factors that predict associated cancer and its prognosis all remain unclear.
Patients and method: During the 30-year period 1969-99, we treated 64 patients who had polymyositis (including two with cancer) and 28 patients who had dermatomyositis (including 10 with cancer). We compared the clinical findings of the patients who had cancer with the findings of those who did not have cancer.
Results: The risk of cancer is significantly higher in dermatomyositis and somewhat higher in polymyositis. An increased cancer risk was found in male patients with dermatomyositis who were older than 50 years. Cancer was diagnosed within 4 years before or after the diagnosis of polymyositis or dermatomyositis, and usually within 1 year. An operation was not possible in many of the patients with cancer because of the advanced stage of the disease.
Conclusion: Our findings suggest that early discovery of malignancy is critical in cases of polymyositis and dermatomyositis.